While fuel injection and other technology have replaced carburetors in most automobiles, carburetors are still used in certain classes of race and high performance vehicles. Carburetors are fuel control devices mounted to an engine intake manifold, which divide and transport the air/fuel mixture into the intake valves. In its simplest form, a carburetor consists of an open pipe through which the air passes into the inlet manifold of the engine. Carburetors use Bernoulli's principle to mix fuel into an air stream, which feeds the engine. Rather than directly controlling the flow of liquid fuel, carburetors meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.
Carburetors may have one or more air induction bores, which are defined by contoured bore walls which converge to form a venturi. Fuel is introduced into the air stream through small holes at the narrowest part of the venturi. The constriction of the air flow through the venturi increases the velocity of air flow, thereby lowering the static pressure, which draws fuel into the airstream through a nozzle or nozzles located in the center of the venturi. Below the venturi is a butterfly valve called the throttle valve—a rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it almost completely blocks the flow of air. The throttle valves control the flow of air through the induction bores and thus the quantity of air/fuel mixture the system will deliver, thereby regulating horse power and speed.
In race and high performance applications, the ability to make quick mechanical adjustments to a carburetor is very desirable in order to accommodate for changing environment and race conditions. Mechanical carburetor adjustments affect the engine's power curve, which represents an engine's horsepower graphed against RPMs, to suit desired performance criteria. Conventional carburetors have a variety of mechanical adjustments for the various valves, jets, boosters and linkages, which allow carburetors to be tuned for optimum performance; however, the complexity, variety and interdependence of these mechanical adjustments are impractical for addressing rapidly changing conditions.
Moreover, even the slightest gains in engine performance are desirable in race and high performance applications. The power curve of any given engine can be affected by a variety of factors, including the speed and nature of the air flow into the induction bores of the carburetor. Turbulent air around the mouth of the carburetor can restrict air flow through the induction bores, resulting in losses in horse power. Conventional carburetor bodies have shaped and contoured surfaces around the mouth of the carburetor that do not transition smoothly into the sidewalls of the induction bores, thereby creating “dead spaces” that disrupt the laminar air flow into the bores. These surfaces produces eddies and turbulent air flow in these “dead spaces” which compromises engine performance. Turbulent air flow into the carburetor can also be exacerbated by the use of an air filter assembly mounted atop the carburetor to filter dust and debris from the inlet air. A typical air filter assembly includes an annular ring type filter seated within a filter housing that mounts atop the carburetor so that air flows radially through the filter, but is then drawn downward into the mouth of the carburetor. Again the radial filter configuration and surface contours of the air filter assembly often hinder laminar airflow into the carburetor, which results in a loss in horse power.